*{margin: 0; padding: 0;}
#nav{
    height: 50px;
    background-color: black;
    overflow: hidden;
}
#main{
    margin: 20px;
}

#tableTop{
    width: 700px;
    height: 40px;
    border: 1px solid black;
    margin: 20px auto;
    line-height: 40px;
    padding-left: 10px;
    box-sizing: border-box;
}
#tableCenter{
    width: 700px;
    height: 40px;
    border: 1px solid black;
    margin: 20px auto;
    line-height: 40px;
    padding-left: 10px;
    box-sizing: border-box;
}
#tableBotm{
    width: 700px;
    height: 200px;
    border: 1px solid black;
    margin: 20px auto;
}
th{
    background-color: skyblue;
    color: #fff;
    height: 50px;
}